According to an inkjet recording method, high speed recording can be performed with a high freedom degree of imaging pattern and a low noise at the time of recording. Further, image recording can be performed at low cost. Still further, the inkjet recording method has advantages such that color recording can be readily performed. Therefore, recently the inkjet recording method is rapidly spreading and further developing. As a recording liquid for the method, hitherto a dye ink, in which a water-soluble dye is dissolved in an aqueous medium, has been widely used. However, the dye ink is poor in water resistance and weather resistance of the resultant printed article. Therefore, studies of the dye ink have been made to improve such disadvantage.
A pigment ink is ordinarily obtained by dispersing a water-insoluble pigment in an aqueous medium. It is general to use a method which includes adding a pigment together with one or plurality of dispersing agents such as various kinds of surfactants or water-soluble polymers to an aqueous solvent, and pulverizing them using a dispersion machine such as a sand mill, a bead mill, or a ball mill, to make the diameter of the pigment particle small to fine (see JP-A-2006-57044 (“JP-A” means unexamined published Japanese patent application) and JP-A-2006-328262). Besides, it is proposed to make pigments a solid solution in consideration of improving a coloring force and weather resistance (see JP-A-60-35055). Further, studies have been made of a method for preparing a pigment dispersion by dissolving an organic pigment together with a polymer dispersing agent or a polymer compound as a dispersing agent in an aprotic organic solvent in the presence of alkali, and then mixing the resultant solution with water (hereinafter the method is referred to as a build-up method), and of the predetermined polymer compounds per se and the like that are used in the above-described method (see JP-A-2003-26972, JP-A-2004-43776, JP-A-2006-342316, and JP-A-2007-119586). However, in the dispersion of pigment particles produced by the build-up method, particle formation so rapidly occurs that it is difficult to control a crystal form of the particles, or to regulate a crystallite diameter. With respect to finely divided pigment particles, it is desired that the pigment particles have a stable crystal form against light and a high crystallinity in consideration of achieving a high resistance to light. As means for achieving such objectives, for example, it is known to use a method of subjecting the pigment particles or the dispersion thereof to a heat treatment or the like (see JP-A-2003-26972).